Optical transceiver design and mechanical features

ABSTRACT

A node for use in a wireless communication network that facilitates alignment of the node with other nodes in the network and a method for aligning the node. The node includes mounting fixtures that enables the mounting of GPS receivers and a tiltmeter to obtain position and bearing information for the node. The node contains alignment features that enable the positioning of an optical transmitter/receiver pair in the node using the data obtained from the GPS receivers and tiltmeter.

The benefit under 35 U.S.C. § 119(e) of the following U.S. provisionalapplications entitled FREE SPACE ALIGNMENT BY GPS, Serial No.60/204,361, filed May 16, 2000, METHOD AND SYSTEM FOR ENCLOSING ANOPTICAL COMMUNICATIONS TERMINAL, Serial No. 60/212,038, filed Jun. 16,2000, and OPTICAL TRANSCEIVER DESIGN AND MECHANICAL FEATURES, Serial No.60/242,220, filed Oct. 20, 2000, is hereby claimed and which are herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to free-space optical communication systems, andin particular, to improved mechanical features that enable alignment ofthe optical transceiver nodes.

2. Description of the Related Art

Over the last several years there has been tremendous growth in thedeployment of fiber-optic facilities by telecommunications carriers suchas Regional Bell Operating Companies (RBOCs), cable carriers, andCompetitive Local Exchange Carriers (CLECs). Deployment of thesefacilities along with the introduction of technologies such as OC-192and DWDM has dramatically lowered the marginal cost of bandwidth on thefiber.

Thus, as a result of this development, there is extensive bandwidth andcommunications capability in carriers' backbone networks. However, manyhomes and offices do not have a practical solution to interface to thesebackbone networks. Consequently, direct attachment of potentialcustomers to these backbone networks remains very expensive.

Currently, there are two practical methods for directly attachingcustomers to backbone networks such as optical fiber networks. These areburied or aerial fiber interconnections and microwave connections.However, both of these methods incur significant up-front costs beforeany revenue can be realized. In the case of buried or aerial fiber,these costs are associated with obtaining rights-of-way for the cableruns, and installing the cable by burying or hanging. In the case of amicrowave system, these up front costs come not only from the costassociated with the microwave repeater equipment, but also from thecosts associated with obtaining rights to the suitable portion of thespectrum. Therefore, system developers and integrators have sought longand hard to find suitable solutions to this “last mile” problem.

Free-space optical communication systems provide a solution to this“last mile” problem. Free-space systems may be designed to use one ormore optical beams, usually generated by lasers, to carry and transmitdata over the free space between two communication terminals or nodes.The transmitting communication node includes one or more lasers togenerate an information-bearing optical beam. The correspondingreceiving terminal or node, which has an optical detector and associatedsignal processing circuit, converts the information into an electricalsignal for further routing or processing. A communication node mayinclude at least one laser and one detector to operate as an opticaltransceiver.

It is desirable to facilitate the initial alignment of the transmittingnode and the receiving node. Additionally, after initial installationhas been completed, it may become necessary to quickly replace a damagedor dysfunctional node with a replacement node. It is further desirableto facilitate reestablishing the communication link by enabling thereplacement node to be pre-aligned so that it can simply be directed topoint to the same location as the transceiver in the node that has beenreplaced.

SUMMARY OF THE INVENTION

One embodiment of the invention is directed to a node for use in awireless communication network. The node includes a base mount deviceconfigured to removably receive a position determination device and atiltmeter, an azimuth plate, an optical receiver/transmitter pairmounted on the azimuth plate and a post. The azimuth plate is rotatablymounted on the post and the post is configured to align the azimuthplate with the base mount.

Another embodiment of the invention is directed towards a system forpositioning and aligning a receiver/transmitter pair of a communicationnode that is part of a wireless communication network. The systemincludes at least one position determination device configured todetermine the position of the positioning system, a tiltmeter,configured to determine the orientation of the positioning system withinthe network, and a node. The node includes a base mount configured toremovably receive a position determination device and a tiltmeter, anazimuth plate, an receiver/transmitter pair mounted on the azimuth plateand a post. The azimuth plate is rotatably mounted on the post ant thepost is configured to align the azimuth plate with the mountinginterface device.

Another embodiment of the invention is directed towards a method ofdirecting a directional transmitter/receiver pair of a node in awireless communications network. The method includes the steps ofassembling a node, wherein the node includes a mounting interface deviceconfigured to removably receive a position determination device and atiltmeter, an azimuth plate, a directional receiver/transmitter pairmounted on the azimuth plate and a post, wherein the azimuth plate isrotatably mounted on the post ant the post is configured to align theazimuth plate with the mounting interface device. The method can includedetermining tolerance offset data for the node, storing the offset datain a memory, installing the node on a fixture at the host site. Theposition and bearing of the node are determined using a positiondetermination device installed on the node, and the pitch and roll ofthe node are determined using a tiltmeter installed on the node. Theoptical transmitter/receiver pair is pointed to the transceivers ofanother node using the offset data stored in the memory, the position,bearing, pitch and roll data.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention willbecome more fully apparent from the following description and appendedclaims taken in conjunction with the following drawings, where likereference numbers indicate identical or functionally similar elements.Additionally, the left-most digit(s) of a reference number identifiesthe drawing in which the reference number first appears.

FIG. 1 is a diagram illustrating an example communication networkaccording to one embodiment of the invention.

FIG. 2 is a perspective view of an embodiment of a node for use in thecommunication network of FIG. 1.

FIG. 3 is an exploded view of the node of FIG. 2.

FIG. 4 is a perspective view of an embodiment of the node of FIG. 2 withGPS receivers mounted on the node.

FIG. 5 is an exploded view of an embodiment of the node with GPSreceivers of FIG. 4 illustrating the mounting features of the node andGPS mounting arms.

FIG. 6 is a perspective view of an embodiment of the node of FIG. 2 witha tiltmeter capable of being mounted on the node.

FIG. 7 is an alternate perspective view of the node and tiltmeter ofFIG. 6 illustrating the mounting features of the node and tiltmetermounting arm.

FIG. 8 a is an exploded view of the lower section of the node of FIG. 2illustrating the base mount and base plate.

FIG. 8 b is an exploded view of the lower section of the node of FIG. 2further illustrating the bulkhead and king post.

FIG. 8 c is a detail view of a section of FIG. 8 b illustrating thev-groove on the king post.

FIG. 9 a is a perspective view of the lower section of the node of FIG.2 with a turret attached to the king post.

FIG. 9 b is a detail view of a section of FIG. 9 a illustrating thev-groove on the king post.

FIG. 10 a is a top elevation view of the turret of FIG. 9 a.

FIG. 10 a is a bottom elevation view of the turret of FIG. 9 a.

FIG. 11 is an exploded view of the upper section of the node of FIG. 2.

FIG. 12 is a block diagram of a method of aligning the node of FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The following presents a detailed description of embodiments of thepresent invention. However, the invention can be embodied in a multitudeof different ways as defined and covered by the claims.

FIG. 1 is a diagram illustrating an example communication network 100.The communication network 100 can include a plurality of nodes 108,interconnected by communication links 110. The network nodes 108 aredisposed on facilities 104. Although only one node 108 is provided perfacility in the example illustrated in FIG. 1, more than one node 108can be provided at one or more of the facilities 104, depending on thecommunication requirements, and also, perhaps, depending on theparticular facility.

Facilities 104 can be buildings, towers, or other structures, premises,or locations. Facilities 104 can, for example, be homes or offices towhich it is desirable to interface one or more backbone networks of oneor more common carriers or service providers. In this exampleembodiment, network 100 can provide the interface between the facilitiesand the backbone network.

Nodes 108 are interconnected with one another by optical communicationlinks 110. In this optical embodiment, nodes 108 can include one or moreoptical transmitters and receivers to provide the communication links110 among the plurality of nodes 108. Additionally, the nodes can beinterconnected with radio frequency communication links. The number oftransmitters and receivers provided at a given node 108 can be varieddepending on the fan-out capabilities desired at that node 108. Theprovision of both a receiver and a transmitter (i.e., transceiver) foreach fan out of the node 108 allows bi-directional communication amongnodes 108.

In one embodiment, each node 108 includes pointing mechanisms such thatthe transmitters and receivers can be rotated to point to a designatedother node 108 as will be discussed below. In one embodiment, suchpointing can be performed in both azimuth and elevation. Ideally, eachtransmitter and receiver can be independently pointed to a designatednode 108.

The network 100 can be implemented and utilized to directly connect aplurality of customers in one or more facilities 104 to a high-capacitycommunication network 116. For example, network 100 can be used toconnect the plurality of customers to a copper or optical fiber backbonenetwork. The network 100 can therefore allow the customers to access ahigh data rate, high-bandwidth communication network from their home,office or other facility, regardless of the existing connectioncapabilities within that facility. Thus, network 100 can be implementedto avoid the need to cable a backbone network over the “last mile” toeach facility 104. The nodes 108 can be connected to the network 100 asdescribed in U.S. patent application Ser. No. 09/181,062 entitled Systemand Method for Integrating a Network Node, filed Oct. 27, 1998, which isincorporated herein by reference in its entirety.

At least one of nodes 108 can be designated as a root node 108A. Rootnode 108A includes additional functionality to interface thecommunication network 100 to a provider network 116 via anothercommunication link 112. The provider network 116 can, for example, be ahigh bandwidth copper or fiber service provider or common-carriernetwork 116.

A root node 108A of the communication network 100 receives acommunication from the provider network 116. The root node 108A acceptsthe communication and, if necessary or desired, reformats thecommunication into a format that can be transported across the networkof nodes 108 and communication links 110. For example, in an examplewhere network 100 is a packet-switched network, root node 108A formatsthe communication into packets suitable for transmission across theoptical communication links 110.

The root node 108A may also determine routing information such that thedata can be sent to the appropriate destination node 108, also referredto as a premise node 108. In a network 100 using packet data, therouting information can be included in the packet header of the packetsbeing sent across network 100. In alternative network geometries, adesignation of the destination node 108 may be used in place of or inaddition to routing information. For example, ring geometries usedestination information as an address for the packets in place ofrouting information.

The root node 108A routes the reformatted data across the network 100 tothe designated destination node 108. The route may be directly todestination node 108 or via one or more intermediate nodes 108, whichare referred to as junction nodes 108 in this capacity. In embodimentsusing packet data, for example, junction nodes 108 may use packet headerinformation to route a received packet to the next node 108.

The destination node 108 receives the data. The received data isforwarded to the end user at the facility 104 associated with thedestination node 108. Prior to forwarding the data to the end user, thedata is reformatted into a telecommunications format such as, forexample, the original format that the data was in when it was receivedfrom provider network 116.

In this example, the fact that the user is interfaced to the providernetwork 116 via the network of links 110 and nodes 108 is preferablytransparent to the user. Communications from the user to the providernetwork 116 can similarly take place, but in the reverse order. Thus,network 100 can provides a two-way connection between one or more usersin one or more facilities 104 with provider network 116. Although onlyone provider network 116 is illustrated in FIG. 1, one or more rootnodes 108A can be used to interface to more than one provider network116 in alternative embodiments.

Thus, a service provider can provide service to users in a plurality offacilities 104 by providing a signal to the root node 108A of thesystem. In one example, nodes 108 use the Asynchronous Transfer Mode(ATM) as the data transport mechanism.

FIG. 2 shows one embodiment of the node 108. Node 108 as shown in FIG. 2includes four node turrets 202, an electronics section 203, a base mount204 and a lid 207. Each node turret 202 includes an azimuth plate 206that is rotatably attached to the node 108 as will be discussed below. Atransceiver 208 to facilitate communication with one or more other nodes108 in the network 100 (FIG. 1) is mounted on each azimuth plate 206. Inone embodiment, there is a single transceiver 208 in each node turret202, and each transceiver 208 provides a communication link 110 (FIG. 1)with one other node 108 in the network 100 at a given time. The fournode turrets 202 allow each node 108 to connect its associated facility104 (FIG. 1) with up to four other nodes 108. Other numbers of turrets202 can be included, depending on the fan-out capability desired for thenode, 108.

Each transceiver 208 can have both a receiver 210 and a transmitter 212,providing two-way communications. However, in alternative embodiments,the transceiver 208 could have just a transmitter 212 or just a receiver210, thereby providing one-way communications. Additionally, it ispossible for one or more node turrets 202 to include more than onetransceiver 208, or an additional receiver 210 or transmitter 212 toprovide additional capabilities, for example such as an RF transceivers.As stated, in one embodiment, the transceivers 208 are opticaltransceivers, however, alternative wireless transceivers can beimplemented operating at wavelengths other than optical wavelengths. Inoptical embodiments, transceivers 208 at nodes 108 can be implementedusing for example, lasers or light emitting diodes (LEDs) as the opticaltransmitters 212 and charge-coupled devices (CCDs), photomultipliertubes (PMTs), photodiode detectors (PDDs) or other photodectectors asthe receivers.

In one class of optical transceiver 208, the optical transmitter 212 andthe optical receiver 210 are fixed relative to each other. Hence, boththe direction of the optical transmitter 212 and the direction of theoptical receiver 210 change in the same manner with the movement of thetransceiver 208. In one embodiment, the transmitter 212 and receiver 210are boresighted to each other during manufacture, such thatbidirectional pointing accuracy can be established and maintained. Thecommunication link between two terminals is established by anacquisition process in which two suitable transceivers 208 respectivelylocated in two different nodes 108 are pointed at each other and arealigned. After the two-way communication is established, information canbe transferred between the two nodes 108. The electronics section 203contains a processor board (not shown) with a controller, for example, amicroprocessor (not shown). The controller points the transceiver 208 aswill be described more fully below.

FIG. 3 is an exploded view of the node of FIG. 2. FIG. 3 illustratesthat the node 108 is generally cylindrical in shape and turrets 202 areenclosed in a cylindrical radome 302. An advantage of the cylindricalshape is that it facilitates the ability to point the turrets 202 toother nodes in a full 360-degree circle. Another advantage of this shapeis that an optical communication beam always passes at a substantiallyright angle with respect to the radome 302 surrounding the node 108,regardless of pointing direction of the turret 202. This helps tomaximize the transmitted beam power. Of course, alternative shapes forthe node 108 can be implemented as well.

The radome 302, in one embodiment, is a clear polycarbonate housing,transparent to the wavelength of the communication link. Alternately,other materials such as acrylic and lexan can be used for the radome302. Additionally, the radome 302 can be tinted, such as deep red, toprovide thermal protection to the inner components. The radome 302 canalso serve as a filter to filter out unwanted noise from wavelengthsother than that of communication link. For example, in one embodiment,where the communication wavelength is 780 nanometers (nm), the radome302 can provide a 780 nm band pass filter. In one embodiment, the radome302 is approximately ⅛^(th) inch thick and twelve inches in diameter,although other dimensions are possible. In one embodiment, the interiorsurface of the radome 302 has a thin Indium Tin Oxide coating that actsas a conductor that allows a current to pass and resistively heat theradome 302 and provide EMI shielding. The radome 302 can be fabricatedfrom two half pieces of polycarbonate material that are joined togetherin such a way as to preserve the clarity of the polycarbonate material.The exterior dimensions of the radome 302 are minimized to the extentpossible based on the size and placement of components of node turret202 to minimize external forces such as wind loads. Alternatively, asingle polycarbonate cylinder can surround each of the node turrets 202in the node stack.

A first custom elastomeric extrusion 303 positioned between theelectrical portion 203 and the radome 302 provides a seal to keep outmoisture or other undesirable elements. In one embodiment, theelastomeric extrusion is positioned in a groove (not shown) in theelectrical portion 203 into which the bottom edge of the radome 302 fitsto provide a good seal. A second custom elastomeric extrusion 305 issimilarly positioned between the lid 207 (see FIG. 2) and the top edgeof the radome 302. The elastomeric extrusions 303 and 305 can be made ofrubber, a rubber-like or polymeric material.

A sunshield 304 is attached to each of the azimuth plates 206 andsurrounds a portion of each turret 202. The sunshield 304 can be ofpolished aluminum to reduce the thermal loading of the node 108. Othermaterials such as mirrored plastic can be used. The sunshield 304 moveswith the azimuth plate 206 so an opening 309 in the sunshield 304remains aligned with the transmitter 212 and receiver 210 allowingoptical beams to reach the transmitter and receiver. Screws 306, snapsor other fasteners attach the sunshields 304 to each turret 202.

Note that in one embodiment, one or more node turrets 202 can beimplemented with the communications equipment to allow them tocommunicate with equipment other than another node 108. This equipmentcan be implemented using, for example, wireless RF communications orother communications techniques. However, in a preferred embodiment,node turrets 202 are dedicated to inter-node communications viacommunication links 110.

The electronics section 203 can include the electronics and mechanics(not shown) to provide the communications interface 112 (FIG. 1)between, for example, the network 116 (FIG. 1) and the one or more nodeturrets 202. In one embodiment, the electronics section 203 provides apath for conducting heat from the node 108. Thus, electronics section203 includes heat fins 308 to help cool the node 108 by convection.

The base mount 204 provides a physical mount with which the node 108 canbe mounted to the facility 104 (FIG. 1). A locating pin hole 310 on thebase mount 204 receives a locating pin (not shown) that is also passedthrough a slot (not shown) on a tripod parapet or other mounting fixtureon the facility 104 (FIG. 1). Thus, the node 108 is oriented withrespect to the facility such that any other node will be placed in theexact same orientation with respect to the tripod parapet at thefacility within the machining tolerance of the slot and locator pin holeas long as the tripod parapet is not altered.

A mechanical interface 314 can be included to provide an interface forpower and signal lines and cables from facility 104 to node 108. Themechanical interface 314 provides a degree of protection from theelements, restricting moisture or other undesirable elements fromgaining access to node 108.

In the case of a relatively narrow beam-width signal, it is desirablethat the transmitter 212 and receiver 210 of a node 108 be pointed witha certain degree of precision to that of another node 108. This isespecially important in applications where communication links areimplemented as optical communication links, where the optical signal hasa relatively narrow beam waist and a small divergence. Additionally,accurate pointing is somewhat dependent on accurate positioning of nodes108 within the network.

The position and bearing information of the subject node 108, coupledwith the position information of other nodes 108 in the network 100,allows pointing information for the node 108 to be determined. Pointingangles for one or more transceivers 208 in the subject node 108 isdetermined with a fair degree of accuracy using this information in asimple triangulation computation. In other words, if the positions ofthe pertinent nodes 108 in network 100 are known, it is astraightforward geometric computation to determine where to point agiven transceiver 208 within the subject node 108, such that thetransceiver 208 is in alignment with a desired other node 108 in thenetwork 100.

Therefore, positioning components can be provided to facilitate theinstallation and integration of one or more nodes 108 within a networksuch as the above-described optical communication network 100. Thesepositioning components are now described in terms of an embodimentsuitable for operation with the above-described optical communicationnode 108. After reading this description, however, it will becomeapparent to one of ordinary skill in the art how the positioningcomponents can be implemented for use in other applications wherepointing or positioning are desired to be achieved with a certain levelof precision.

FIG. 4 illustrates an example implementation of two global positioningsystem (GPS) receivers 402 (a) and (b) mounted on the node 108. In oneembodiment, each GPS receiver 402 is capable of receiving GPSpositioning information to enable determination of a location of thenode turret 202. In one embodiment, differential GPS is used to obtainincreased accuracy in position determination over that of conventionalGPS receivers. In certain embodiments using differential GPS, theposition determination can be made to the meter or sub-meter accuracylevel. The GPS receivers 402 each provides X, Y and Z positiondetermination relative to an earth-based reference such that the exactlocation of the positioning system can be determined.

In one embodiment, the service for the differential GPS receiver 402 isprovided by Fugro's Omnistar service. This service utilizes ageostationary satellite to provide positioning information good toapproximately one meter. Other positional systems can be used such as,for example, DCPGPS, traditional non-differential GPS, loran, or otherpositioning services or devices. Although a node 108 can be manuallysurveyed by a surveyor for position determination, it is preferable thatan automated device such as, for example, a GPS receiver 402 beutilized. Such devices enable automated and more rapid positiondetermination of the positioning system. Once determined, the positioninformation, usually expressed in terms of position coordinates (e.g.,X, Y, Z position), is provided a network controller (not shown) so thatposition coordinates from the various nodes 108 can be correlated andpointing information calculated.

The position data can then be used by the nodes 108 for orientationpurposes. Each transceiver 208 can be automatically oriented to point toa desired transceiver 208 in another node based on the position data.

The GPS receivers 402 are attached to the base mount 204 with GPSmounting arms 404. It is desirable that the GPS receivers 402 beprecisely attached in a determined configuration such that positionalinformation for the GPS receivers can be converted into accurateposition information of the node. In one embodiment, two GPS receivers402(a) and 402(b) on two GPS mounting arms 404(a) and 404(b) areattached to the base mount 204. The mounting arms 404 are attached tothe base mount approximately 180 degrees apart to maximize theseparation between the GPS receivers 402. To increase the portability ofthe GPS mounting arm 404, each mounting arm includes an outer portion408 and a telescoping inner portion 410 that retracts into the outerportion 408. The GPS receiver 402 is mounted to a first end 412 of theinner portion 410. The inner portion 410 contains a groove 414 along asubstantial length of one side of the inner portion 410. A set pin 416travels within the groove 414 and engages a first locking hole (notshown) within the groove 414 in a second end 420 of the inner portion410 to lock the mounting arm 404 in an extended position. The set pin416 engages a hole 418 in the first end 412 of the inner portion 410 tolock the mounting arm 404 in a stowed position. One skilled in the artwill be able to conceive of alternative ways to provide telescoping orfolding features to the mounting arm to increase the portability of thearm, and these alternative ways likewise should be considered part ofthe invention.

FIG. 5 illustrates that an embodiment of the mounting arm 404 includes amounting end 502 with a clamp head 506. The claim head 506 is attachedto one end of a clamp shaft 508. A handle 510 is attached to a secondend of the clamp shaft 508. The mounting end 502 of the GPS mounting arm404 is configured to engage a keyhole 512 in a mounting box 514 on thebase mount 204. The keyhole 512 is precision machined in the mountingbox 514 and the mounting box is precision mounted to the base mount 204so that accurate alignment is maintained between the GPS receivers 402and the base mount 204. This allows positional information received bythe GPS receivers 402 to be translated into positional information forthe node 108.

The keyhole 512 has an upper circular portion 516 with a circumferencelarger than the circumference of the clamp head 506 and a lower portion518 in communication with the upper portion 516 that has a circumferencesmaller than the. circumference of the clamp head 506. The clamp head506 is inserted into the keyhole 512 such that the clamp head 506 isreceived into the mounting box 514 through the upper portion 516 of thekeyhole 512. The GPS mounting arm 404 is then slid downwards such thatthe shaft 508 of the clamp head 506 is positioned in the lower portion518 of the keyhole 512, such that a flat rear surface 520 of the clamphead 506 contacts the mounting box 514 preventing withdrawal of theclamp head 506. The handle 510 is manipulated to retract the clamp head506 such that a frictional fit is achieved locking the mounting arm 404onto the base mount 204.

The mounting end 502 also includes an alignment guide pin 522 extendingfrom the mounting arm 404. The alignment guide pin 522 is received in afirst alignment slot 524 in the mounting box 514. The alignment guidepin 522 and alignment slot 524 configuration allows the mounting arm 404to be attached to the node 108 in a single alignment orientation. Inthis embodiment, the alignment guide pin 522 and alignment slot 524allow a technician installing the GPS receiver 402 onto the node 108 toensure that the two pieces are properly aligned with one another. Thesecomponents can further insure that this alignment does not change duringthe installation process.

In one embodiment, the GPS mounting arm 404 is of sufficient length toprovide a one-meter separation between the GPS receivers 402 and thenode. The two GPS receivers 402 are positioned on opposite sides of thenode 108, or 180 degrees apart, such that there is a two-meterseparation between the GPS receivers 402 when obtaining the positionmeasurements. The use of two GPS receivers 402 separated by a determineddistance allows the bearing of the node 108 to be determined.Alternately, other lengths of mounting arms 404 can be used to provide agreater or smaller separation. The mounting arms 404 can be anodized andTeflon coated to provide durability.

In one embodiment, the GPS receivers 402 provides a bearing relative togeographic north. Tiltmeter 602 provides a bearing to ⅓ degree to ½degree of accuracy, which as discussed below, is sufficient to allowtransmitters 212 and receivers 210 to be initially pointed to thedesired node 108. Alternative accuracy ranges can be used depending onthe distance between nodes 108, transmit beam divergence, and receiveraperture.

Once the positional information has been obtained, the GPS receivers 402can be removed from the node 108. In this embodiment, the mounting arms404 are provided such that they can be easily released from the node 108after the position data is obtained. The removal can be done withouthaving to be concerned that the position and orientation of the node 108has been affected or altered due to the removal of the mounting arms404. In yet another alternative, each node 108 can include at least oneGPS receiver permanently attached to the node to enable the initialpointing operations. However, this alternative may be undesirable as thecosts of the GPS receivers are incurred for each of the nodes 108 havingthese components. Therefore, it is advantageous that these GPS receivers402 and mounting arms be removable from the node 108.

FIGS. 6 and 7 illustrate a second part of the positioning system, whichincludes a tiltmeter 602 that can be mounted to the base mount 204 insimilar fashion as the GPS receivers 402. After the GPS receivers 402and GPS mounting arms 404 have been removed, one of the mounting boxes514 previously used to receive one of the GPS mounting arms 404 is usedto receive the tiltmeter 602. The tiltmeter 602 is mounted on atiltmeter mounting arm 604. The tiltmeter mounting arm 604 has amounting end 605 with a clamp head 606 attached to a first end of ashaft 608 similar to the GPS mounting arm 404 of FIG. 4. A handle 610 isattached to a second end of the shaft 608.

The clamp head 606 is received in the upper portion of the keyhole 512and is slid into a locking position as described above with respect tothe GPS mounting arm 404. The mounting end 605 of the tiltmeter 602includes two alignment guide pins 722 and 723. The first alignment guidepin 722 is received into the first alignment slot 524 that was also usedin conjunction with the GPS mounting arm 404 (of FIG. 4). The secondalignment guide pin 723 is received in a second alignment slot 725 inthe mounting box 514. In one embodiment, only one mounting box 514 onthe node 108 contains the second alignment slot 725 such that there isonly one mounting box 514 that will receive the tiltmeter mounting arm604. This ensures that the tiltmeter 602 is installed in the desiredorientation with respect to the node 108 and that the two components areproperly aligned with one another in a repeatable manner. The alignmentguide pins 722 and 723 and alignment slots 724 and 725 further insurethat this alignment does not change during the installation process.

The tiltmeter 602 provides a determination of the pitch and roll.Because the tiltmeter 602 is aligned with the base mount 204 through thetiltmeter mounting arm 604 and mounting box 514, the pitch and roll ofthe tiltmeter 602 can be used to determine the pitch and roll of node108. Therefore, it is advantageous to have only a single point ofattachment on the node so that the orientation of the node can beaccurately determined. Thus, in this embodiment, the tiltmeter 602 canprovide information important to the leveling of the node 108 to whichthe tiltmeter 602 is attached. For example, roll and pitch informationcan be used to determine whether the node 108 is level, or how far offof level the node is. This leveling information can be used to helplevel the node, or can be provided to the pointing systems to allow theroll and pitch offsets of the node to be taken into account indetermining pointing angles to other nodes. From this information, thepointing of the one or more transceivers 208 with node 108 can also bedetermined. The tiltmeter 602 can be a tiltmeter such as those availablefrom Applied Geomechanics.

As one skilled in the art can envision, other methods of preciselyaligning the GPS receivers 402 and tiltmeter 602 to the node 108 can beused. For example, a precision-machined slot 730 can be machined intolower edge of base mount 204. A clamp (not shown) can be used to attachthe mounting arms to the base. The precision-machined slot clocks themounting arms 404 and 604 to the base amount 204 in such a way thatprecise alignment and registration is achieved and accurate positioninformation is translated to the node.

The position and alignment information is translated from the GPSreceivers and tiltmeter 602 to the base mount 204 as described above.Precision aligned components in the node translate this information tothe turrets 202 as will be described with reference to FIGS. 8-10. FIG.8 a illustrates one embodiment of the construction of the lower portionof the node 108. The base mount 204 includes a substantially circularbase plate 802. The base plate 802 is provided with an opening 803covered by a Gore-Tex patch (not shown) that allows the passage of airinto and out of the node 108, thus allowing the pressure in the node 108to equalize with the surroundings, reducing pressure differences thatcould be caused by daily and seasonal barometric loading. The patch canalso be made from other breathable materials. Pillars 804 attach acircular bulkhead 806 (FIG. 8 b ) to the base plate 802. In oneembodiment, four pillars 804 are used. A first end 808 of each pillar804 is attached to the base plate 802 with screws 810 or otherfasteners. FIG. 8 b illustrates that a second end 812 of each pillar 804is attached to the bulkhead 806 with screws 814 or other fasteners.Screw holes 816 in the base plate 802 and the bulkhead 806, as well asthe pillars 804, are aligned and precision-machined so that the bulkhead806 is properly aligned with the base mount 204.

The bulkhead 806 has a circular hole 818 in the center therein. A kingpost 820 is inserted through the hole. The king post 820 is a hollowtube used to distribute electrical leads and cables, including power,to/from the turrets 202 (see FIG. 2) and the base mount 204. FIG. 8 c ,a detail section from FIG. 8 b , illustrates that the king post 820 hasat least one, ideally two, precision-machined v-groves 822 running asubstantial length of the king post 820. “V” point set screws pass 824through holes 826 in a neck 828 in the bulkhead 806 around the circularhole 818 and engage the king post v-groove 822, thereby aligning theking post 820 with respect to the bulkhead 806 and thus the base mount204.

Returning to FIG. 8 b , the king post 820 is secured into position withrespect to the bulkhead 806 by a spiral retaining ring 830. The spiralretainer ring 830 fits in appropriately sized groove (not shown) in theexterior surface of the lower end portion 832 of the king post 820. Theretaining ring 830 is a non-expanding double-spiral retaining ring. Theretaining ring 830 has a circumference larger than the circular hole 818such that the retaining ring 830 prevents the king post 820 from beingpulled through the circular hole 818.

FIG. 9 a illustrates that the turrets 202 are stacked above the bulkhead806. As mentioned above, in one embodiment, node 108 contains fourturrets 202. Each turret 202 has an azimuth plate 206 and an inner hubgear 902 with a precision center bore (not shown) therein such that theking post 820 is received in the hole. FIG. 9 b , a detail section ofFIG. 9 a , illustrates that the inner hub gear 902 slides over the kingpost 820 and is aligned to the king post 820 using set screws (notshown) that pass through precision aligned vertical slots 905 in theinner hub gear 902 and engage the v-grove 822 of the king post 820. Theset screws (not shown) align the turret 202 to the king post 820. Theazimuth plate 206 is rotatably attached to the inner hub gear 902 suchthat the azimuth plate 206 can rotate around the king post 820.

FIG. 10A illustrates a top view embodiment of the turret 202. An azimuthstepper motor 1002 is mounted on the azimuth plate 206. FIG. 10B is abottom view of the turret of FIG. 10A and illustrates that the azimuthstepper motor 1002 is attached to a spur gear 1004 that meshes with aplanetary gear 1006 mounted on the inner hub gear 902. The spur gear1004 and the planetary gear 1006 driven by the azimuth stepper motor1002 control the rotation of the azimuth plate 206 around the king post820. In one embodiment, the azimuth stepper motor 1002 can rotate theazimuth plate 206 a total of 370 degrees about an axis in line with theking post 820. In this embodiment, the motor maintain its position, evenwhen its drive coils are not energized.

An elevation linear stepper motor 1008 is mounted on the azimuth plate206. The elevation stepper motor 1008 attaches to a rod 1010 thatcontrols the elevation of the transceiver 208. In one embodiment, theelevation stepper motor 1008 is a linear actuator stepper motor thatcannot be back driven with a 0.00025 inch advance per step giving 150microradians (μrads) per step. The elevation stepper motor 1008 in oneembodiment provides a field of movement of ±20 degrees. Thus, providedanother node 108 (not shown) is within the line of sight of transceiver208, and within ±20 degrees of elevation, the two nodes 108 can becommunicably connected.

The stepper motors 1002 and 1008 cause the transceiver 208 to rotate inazimuth or elevation in discrete steps. The transceiver 208 can bedriven to a resolution that is approximately 10 times finer than thedivergence of a transmit laser (not shown). Thus, in one embodimentwhere the divergence of the transmit laser beam is 1.5 mrads, theresolution of the gimbals is about 150 microradians (μrads). The steppermotors 1002 and 1008 are connected to a controller (not shown) in theelectronics section 203 (see FIG. 2). The controller directs themovement of the stepper motors 1002 and 1008.

In an alternate embodiment, the stepper motors 1002 and 1008 drivetoothed timing belts (not shown) that move the transceiver 208 throughtoothed pulleys (not shown) with a toothed belt arrangement thatprovides an arrangement that minimizes belt slippage. Other drivemechanisms can also be utilized.

The motors have about 1.57 mrad per step resolution and an appropriateturn-down ratio. In one embodiment, the azimuth turn-down ratio is 10:1,and the elevation ratio is 12:1. In one embodiment, the azimuth steppermotor 1002 has an internal gear drive train ratio of 30:1, and with theplanetary gear 1006, provides a total ratio of 300:1 to reduce the motorarmature motion.

To provide for the precise control drive necessary for smooth operationof the transceiver 208, a first constant tension tensioner spring 1012is provided to minimize backlash between the gears connecting theazimuth plate and throughout the drive train of the azimuth steppermotor. As is known, backlash can be defined as play between the gearteeth of intermeshing components such as the gears. Should backlash beevident in the control drive means for the turret 202, the positioningof the turret 202 would be less accurate in that backlash would allowthe turret 202 to move in an indeterminate amount. The tensioner spring1012 takes out the backlash by causing the teeth of the gears to ride onthe same side of the opposing gear when stationary, independent of thepreceding direction of travel.

The tensioner spring 1012 is coupled between the inner hub gear 902 anda suitable support on the azimuth plate 206. The tensioner spring 1012is connected to a spool 1014 and is coiled thereabout and the spool 1014is rotatable about the inner hub gear 902. The tensioner spring 1012 isadapted to impose a substantially constant bias upon all gearsthroughout the drive train of the azimuth stepper motor 1002, includingthe planetary gear 1006 and the spur gear 1004. As the planetary gear1006 is rotated via the spur gear 1004, the tensioner spring 1012 coilsabout or uncoils from the spool 1014 maintaining the bias upon the gearholding the gear teeth in mesh with the adjacent gear teeth. In thisfashion, backlash is prevented. A second tensioner spring 1016 isprovided to minimize backlash in the elevation stepper motor.

FIG. 11 is an exploded view of the node of FIG. 2, and illustrates thatabove the upper-most turret 202, a loading post 1102 is inserted into ahollow second end 1104 of the king post 820. A shear pin 1106 isinserted through holes 1108 in the kingpost 820 and in holes 1110 in theloading post 1102 to attach the loading post 1102 to the king post 820.

A lid 1112 is slid over the loading post 1102. The lid is configuredwith an airspace 1116 for convective cooling of the node 108. Theloading pin 1102 passes through a circular hole in the lid 1112.

A spring 1118 is placed over the lid 1112. An EMI shield 1120 and a topcap 1122 are placed over the spring 1118. A tensioning screw 1124 isinserted through the top cap 1122 and engages threads (not shown) in theloading post 1102. Threading the tensioning screw 1124 into the loadingpost 1102 compresses the spring 1118. The compressed spring 1118provides a on force on the lid 1112 that seat the radome 302 in thegroove (not shown) in the lid 1112 and further seats the radome 302against the electrical section 203 such that a weather tight seal ismaintained around the radome 302 through daily variations intemperature. The king post 820 and the radome 302 are held in opposingtension and compression, respectively, to minimize titling of thekingpost 820 and provide stiffness. This minimizes alignment variationon the turrets 202 caused by the tilting of the kingpost 820 after thenode 108 has been assembled. A rubber cap 1126 is secured over thetensioning screw 1124 to provide a weathertight boundary. A top cap 1128is placed over the lid 1112, covering the rubber cap 1126. The top cap1128 can be made of a light colored plastic to reduce the solar thermalload. In one embodiment, the shape of the cap 1128 sheds water away fromthe radome 302 and minimizes wind loads discourages perching of birds.

Preferably, there is sufficient space above the upper-most turret 202 toprovide adequate air circulation. A thermoelectric or other temperaturecontrol device can be provided to maintain a desired equilibriumtemperature. In one embodiment, an equilibrium of approximately 12degrees C. above the ambient temperature is preferred to minimizecondensation of ambient air.

After assembly of the node 108, a tolerance offset data value can bedetermined to account for summation of machining tolerances. Forexample, the tolerance offset could account for machining tolerances inthe various components described above that connect the GPS receivers402 and tiltmeter 602 to the base mount 204 and the components thatconnect the turrets 202 to the base mount 204, such as the king post 820and pillars 804. The tolerance offset could also account for machiningvariations in attaching the transceiver 208 to the turret 202 throughthe stepper motors 1002 and 1008 and gears 1004 and 1006. By combiningthe mechanical components of the node 108 as described above andaccounting for any actual offset from design values, a precisedetermination of the pointing direction for each transceiver 208 can beaccomplished. The offset data values are stored in a non-volatile randomaccess memory (RAM) (not shown) in the processor board. The node 108 canthen be shipped and installed on a tripod parapet at a facility 104 (seeFIG. 1) via the locating pin and set screws 310 as described above.

The three pieces of orientation data for a node, i.e., the X, Y, and Zposition data and bearing from the GPS receivers, the pitch and rollinformation of the node from the tiltmeter 602 and the offset datastored in the RAM, are used to point the receiver 210 and transmitter212 to another node 108 in the network. The orientation data can be sentto a central facility via a phone line or other communications network.The central facility can perform the mathematical calculations using theorientation data and the known location of the target node to calculatepointing directions to align the nodes. The central facility can supplythe pointing directions back to the node as directions to the azimuthand elevation stepper motors. Therefore, there is the ability to quicklyinstall and align a node 108. There is also an ability to replace nodesat a facility in the event the installed node becomes damaged ordysfunctional, allowing the link to other nodes in the network to berapidly re-established.

A method of installing or replacing a node 108 in the network accordingto an embodiment of the invention is now described with reference toFIG. 12. In step 1202, one or more nodes are assembled as describedabove. In step 1204, the tolerance offsets for the individual node aredetermined and stored in the RAM. For example, the tolerance offsetscould account for machining tolerances in the various componentsdescribed above that connect the GPS receivers 402 and tiltmeter 602 tothe base mount 204 and the component that connect the turrets 202 to thebase mount 204, such as the king post 820 and pillars 804. The toleranceoffset could also account for machining variations in attaching thetransceiver 208 to the turret 202 through the stepper motors 1002 and1008 and gears 1004 and 1006. In step 1206, the node is installed on atripod parapet using the locating pin and slot on the tripod parapetsuch that any other node will be placed in substantially the sameorientation. Alternatively, the node can be attached to a bracket orother structure having a locating pin and slot. In step 1208, the GPSreceivers are attached to the node using the keying fixtures as thealignment fixture. In step 1210, X, Y, and Z positional information isobtained. In step 1212, the GPS receivers are removed from the node.

In step 1214, the tiltmeter 602 is attached to the node using the keyingfixtures as the alignment fixtures. In step 1216, the bearing of thenode is obtained. In step 1218, the tiltmeter 602 is removed from thenode. In step 1220, the offset data from the RAM, the position data andthe bearing data are used to guide each turret 202 on the node to pointto the desired other node. In step 1222, if the node becomesdysfunctional or needs to be replaces for some other reason, the node isremoved and the replacement node is installed in its place using thelocating pin and slot as keying fixtures. In step 1224, the offset datafrom the replacement node RAM is combined with the position data andbearing data previously obtained and used to guide each turret 202 onthe replacement node to point to the desired other node.

Specific blocks, sections, devices, functions and modules have been setforth. However, a skilled technologist will realize that there are manyways to partition the system of the present invention, and that thereare many parts, components, modules or functions that may be substitutedfor those listed above. While the above detailed description has shown,described, and pointed out the fundamental novel features of theinvention as applied to various embodiments, it will be understood thatvarious omissions and substitutions and changes in the form and detailsof the system illustrated may be made by those skilled in the art,without departing from the intent of the invention.

1. A node for use in a wireless communication network, the nodecomprising: a base mount configured to removably receive a positiondetermination device and a tiltmeter; at least one azimuth plate; anoptical receiver/transmitter pair mounted on the azimuth plate; and apost, wherein the azimuth plate is rotatably mounted on the post and thepost is configured to align the azimuth plate with the base mount. 2.The node of claim 1, wherein the post includes a groove.
 3. The node ofclaim 2, wherein the groove is a V-groove, wherein the V-groove isconfigured to receive a set screw that aligns the azimuth plate to thepost.
 4. The node of claim 1, further comprising a plurality of azimuthplates rotatably mounted on the post.
 5. The node of claim 1, whereinthe post further comprises a conduit for transmitting signals to thetransmitter/receiver pair.
 6. The node of claim 1, wherein the basemount precisely aligns the position determination device and tiltmeterto the post.
 7. The node of claim 1, wherein the base mount comprises afirst mounting box with a keyhole configured to receive a portion of theposition determination device.
 8. The node of claim 7, furthercomprising a second mounting box, wherein the first mounting box has twoslots proximate the keyhole to receive guide pins, and the secondmounting box has one slot proximate the keyhole to receive a singleguide pin.
 9. The node of claim 1, further including a radome and a lidsurrounding the optical receiver/transmitter pair.
 10. The node of claim9, further comprising a tensioning screw and a spring configured toplace the post in tension and the radome in compression.
 11. The node ofclaim 9, wherein the base mount includes an opening covered by abreathable patch.
 12. The node of claim 9 further containing a heaterelement to prevent condensation on the radome.
 13. The node of claim 1,wherein the azimuth plate further comprises an azimuth stepper motor toadjust the azimuth pointing direction of the receiver/transmitter pair.14. The node of claim 13, further including a constant tension spring toreduce backlash in the stepper motor.
 15. The node of claim 13 where theazimuth stepper motor is configured to provide at least 360 degrees ofrotation to the transmitter/receiver pair.
 16. The node of claim 1,wherein the azimuth plate has an elevation stepper motor configured toadjust the elevation pointing direction of the receiver/transmitterpair.
 17. The node of claim 16, further including a constant tensionspring to reduce backlash in the elevation stepper motor.
 18. The nodeof claim 16 where the azimuth stepper motor is configured to provide atleast 20 degrees of elevation movement to the opticaltransmitter/receiver pair.
 19. The node of claim 1, further comprising anon-volatile memory device to store data that accounts for offsets inthe actual pointing direction of the optical receiver/transmitter pairrelative to a design pointing direction.
 20. A system for positioningand aligning a receiver/transmitter pair in a communication node, withsaid node part of a wireless communication network, the systemcomprising: a position determination device configured to determine theposition and bearing of the positioning system; a tiltmeter, configuredto determine the pitch and roll orientation of the positioning systemwithin the network; a base mount configured to removably receive theposition determination device and the tiltmeter; at least one azimuthplate; an optical receiver/transmitter pair mounted on the at least oneazimuth plate; and a post, coupled to the base mount and wherein theazimuth plate is rotatably mounted on the post ant the post isconfigured to align the azimuth plate with the base mount.
 21. Thesystem of claim 20, wherein the position determination device comprisestwo GPS receivers.
 22. The system of claim 20, wherein the positiondetermination device is a differential GPS (DGPS) receiver.
 23. Thesystem of claim 22, wherein there are two DGPS receivers.
 24. The systemof claim 20, wherein the tiltmeter is further configured to determineroll and pitch angles of the node.
 25. The system of claim 20, whereinthe position determination device removably attaches to the base mount.26. The system of claim 20, wherein the tiltmeter removably attaches tothe base mount.
 27. The system of claim 20, wherein the base mountcomprises a first mounting plate and a second mounting plates, whereinthe tiltmeter attaches to the first mounting plate.
 28. A method ofpointing a directional transmitter/receiver pair of a communication nodein a wireless communications network, wherein the node comprises a basemount configured to removably receive at least one position determiningdevice and a tiltmeter, an azimuth plate, a directionalreceiver/transmitter pair mounted on the azimuth plate, and a post,wherein the azimuth plate is rotatably mounted on the post and the postis configured to align the azimuth plate with the base mount, saidmethod comprising: determining tolerance offsets data for the node;storing the offset data in a memory; installing the node on a fixture;determining the position and the bearing of the node using a positiondetermination device installed on the node; determining the pitch androll of the node; and pointing the optical transmitter receiver pair toa transceiver of another node using the offset data stored in thememory, the position, bearing, pitch and roll data.
 29. The method ofclaim 28, wherein the tolerance offset data accounts for machining andassembly variations in the base mount, azimuth plate and post.
 30. Themethod of claim 28, further including the step of removing the GPSreceivers after the positional and bearing information is obtained. 31.The method of claim 28, further including the step of removing thetiltmeter after the pitch and roll information is obtained.